Windshield wiper motor link depressed park mechanism

ABSTRACT

A windshield wiper drive mechanism that functions to park the windshield wiper arms and blades outside the normal run pattern, i.e., in a depressed park position, by extending the effective wiper motor output arm radius. The effective output arm radius is controlled through a rotation sensitive, spring-loaded, double latch means carried on an eccentric interposed between the output arm and a driving link connected to the wiper arm linkage.

EJnited States Patent Beard et a]. 1 1 May 30, 1972 WINDSHIELD WIPERMOTOR LINK 2,489,626 11/1949 Doucette ..74/527 DEPRESSED PARK MECHANISM2,945,385 7/1960 Nelson ..74 75 [72] inventors: Kenneth A. Beard, AnnArbor; Theodore P i r aminerwilliam F. O'Dea y Deal'bom; Gordon J gg r,Assistant Examiner-Wesley S. Ratliff, Jr. H1ghland Park, all of Mich.Attorney-John R. Faulkner and John .I. Roethel [73] Assignee: Ford MotorCompany, Dearborn, Mich. [22] Filed: Sept. 11, 1970 [57] ABSTRACT Awindshield wiper drive mechanism that functions to park [2]] Appl' 71532the windshield wiper arms and blades outside the normal run pattern,i.e., in a depressed park position, by extending the cf- 52 U.S. c1 ..7475,15/250.27 fictive Wiper radius- The effective-WW 511 lm. c1 ..F16h 2140 radius is through a Spring 58 Field of Search ..74/75, 527; 15 2502?waded double latch means carried eccentric ime'Pmd between the outputarm and a driving link connected to the [56] References Cited wperUNITED STATES PATENTS 4 Claim 6 Drawing 2,733,609 2/1956 Latta ..74/75 1/1 il 5731 *7/ i ,I A" r l 1 5 11 42 I i2 I l 4 9 ,5; 0/ j/ /j j 4: T /71 1 5,; El 1 1 j J I 7 4/ 4/ 4 3* Patented May 30, 1972 3,665,772

2 Sheets-Sheet l BY wm Patented May 30, 1972 3,665,772

2 Sheets-Sheet 2 WINDSIIIELD WIPER MOTOR LINK DEPRESSED PARK MECHANISMBACKGROUND OF THE INVENTION The present invention is concerned with awindshield wiper drive mechanism having provision for parking thewindshield wiper arms and blades outside the normal run or wipe patternor in what is commonly referred to as a depressed park position. Thedesirability of a depressed park position'for the wiper blades is welldocumented in the prior art. Basically, the purpose is to position theblades when not in use below the line of sight through the windshield bybringing the blades down to the top of the reveal molding or, in thecase of the concealed part wiper systems, below the level of the uppersurface of the cowl.

The prior art discloses at least two ways to mechanically achieve adepressed park system which may be categorized as l adirection-sensitive linkage-lengthening arrangement and (2) a crank armvarying mechanism. U.S. Pat. No. 2,717,518, issued Sept. 13, 1955 toEdward Latta, is exemplary of a direction-sensitive linkage-lengtheningarrangement for use in depressed parking of windshield wipers. US. Pat.No. 2,866,344, issued Dec. 30, 1958 to Elmer E. Reese, discloses amechanical movement for actuating a windshield wiper and particularly acrank assembly for converting rotation to oscillation including meansfor varying the throw of a crank so as to vary the amplitude ofoscillation imparted to the wiper blades.

The mechanism disclosed herein has characteristics of both types but forpurposes of description will be considered as being primarily a crankarm varying mechanism in which the depressed park feature is achieved byincreasing the windshield wipe pattern during the park cycle byextending the wiper motor output arm radius. It is an object of thepresent invention to provide a simplified and positive acting mechanismadapted to accomplish the desired result.

SUMMARY OF THE INVENTION The windshield wiper drive mechanism embodyingthe present invention has a shaft rotatable by a reversible motor. Awiper motor output arm is fixed to the shaft and carries a drivepin. Themechanism also includes a driving link coupled to a wiper arm linkage.Interposed between the output arm and the driving link is an eccentric,the latter being rotatable about the drivepin and the driving link beingrotatably coupled to the eccentric for rotation about an axis displacedfrom the axis of rotation of the eccentric about the drivepin.

The effective output arm radius for normal wiper pattern operation isthe distance from the shaft axis to the drivepin and for depressed parkposition the effective output arm radius is increased by the distancebetween the drivepin and the axis rotation of the driving link on theeccentric. The improvement embodied in the present invention comprises adouble latch device carried by the eccentric having a pair ofspring-loaded latch elements which lock the output arm to the eccentricin the depressed park or maximum output arm radius condition of theoutput arm. Upon initiation of the run cycle from depressed parkposition of the wiper arm one of the latch elements unlocks while theother remains locked until the end of the first half cycle of the runcycle is reached to restore the effective output arm radius to normalwipe pattern radius. The second latch element then unlocks the eccentricfrom the arm and locks the eccentric to the drivelink. With theeccentric locked to the drivelink, relative rotation of the eccentricabout the drivepin occurs and a normal wiper pattern sweep of the wiperarm is obtained.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of thewindshield wipe pattern of the windshield wiper drive mechanismembodying the present invention;

FIG. 2 is a vertical section of the eccentric and latch means forvarying the output arm effective radius;

FIG. 3 is a view in part similar to FIG. 2 illustrating the eccentricand latch means in a second operative position;

FIG. 4 is an enlarged section view on the line 4-4 of FIG. 2;

FIG. 5 is an enlarged section view on the line 5-5 of FIG. 2; and

FIG. 6 is an enlarged section view on the line 6-6 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings,FIG. 1 diagrammatically illustrates the wiper pattern to be controlledby the windshield wiper drive mechanism, generally designated 10,embodying the present invention. FIG. 1 is a view as seen from theinside of the vehicle looking toward the front through the windshield.The directions of rotation and swinging movement will be described fromthis viewpoint.

The output arm 11 of the drive mechanism is connected to a drivelink 12through an eccentric and latch means to be hereinafter described. Thedrivelink .12 is connected to a wiper linkage system that includes apivoted link 13 and a transfer link 14 connected to a second pivotedlink 15. The pivoted links 13 and 15 are in turn connected to thesupport arms 16 for the left side wiper blade 17 and for the right sidewiper blade 18 which are shown in their depressed or park position.

The normal wiper pattern for the left side wiper blade 17 extends fromthe line 19 to the line 21 and for the right side wiper blade 18 fromthe line 22 to the line 23. Stated another way, the lines 19 and 22correspond to the 0 rotation position of the output arm 11. When thelatter has travelled through of rotation, the wipers 17 and 18 reach thepositions indicated by the lines 21 and 23, respectively. As the outputor crank arm 11 completes 360 of rotation the wipers 17 and 18 return tothe positions indicated by the lines 19 and 21, respectively. As noted,the wipers 17 and 18 are shown in their parked position which is aposition somewhat below the positions indicated by the lines 19 and 21.This park position is obtained by reverse rotation of the output arm 11.

In FIG. 1, the normal or run cycle of the output arm 11 is indicated bythe arrow 24 and the reverse or park cycle of the output arm 11 isindicated by the arrow 25. During normal or run cycle wiper patternoscillation the pivoted link 13 travels between the dotted lines 13a and13b and the pivoted link 15 between the dotted lines 15a and 1512. Todrive the wiper blades to the park positions 17 and 18, respectively, itis necessary to drive the pivoted links 13 and 15 to the solid linepositions shown in FIG. 1. In the wiper drive mechanism embodying thepresent invention, this is accomplished by increasing the output arm 11effective radius in a manner best explained with reference to FIGS. 2and 3. Referring first to FIG. 3, the components of the drive mechanism10 are shown in normal wipe pattern drive position. First, it should beexplained that the output or crank arm 11 is secured to the windshieldwiper system motor output shaft 26. The motor is a reversible electricmotor and is controlled by circuitry which upon the on switch beingactuated causes it to rotate in a run cycle drive direction, i.e., in aclockwise direction as indicated by the arrow 24 in FIG. 1. When the onswitch is turned back to the off position, the motor reverses directionand rotates in a counterclockwise direction as indicated by the arrow 25in FIG. 1. The motor is stopped at a predetermined position to park thewiper blade against the bottom edge of the windshield. As an example ofthe manner in which the motor operation may be so controlled, referencemay be made to US. Pat. application Ser. No. 735,135, filed June 6, 1968by Eugene C. Gagnon et al. now US. Pat. No. 3,532,952 issued Oct. 6,1970, for Internal Switching Mechanism to Reverse and Dynamically Brakethe Motor for Parking the Wipers.

The crank arm 11 carries a drivepin 27 about which an eccentric 28 isrotatably joumalled. The eccentric 28 has an upwardly projectingcylindrical extension 29 the center or axis of which is laterally offsetfrom the axis of the drivepin 27. The drivelink 12 is provided at itsend.3l shown in FIG. 3 with a circular aperture 32 which fits over thecylindrical extension 29 of the eccentric 28. A snap ring 33 holds thedrivelink end 31 on the eccentric 28 and the latter is held on thedrivepin 27 by a second snap ring 34. With the foregoing arrangement,the axis of rotation of the eccentric 28, as determined by the drivepin27 is in fixed, spaced, parallel relation to the axis of the shaft 26.

A latch means including a pair of latch elements or latch pins 35 and36, is carried on the eccentric 28, the latch elements 35 and 36 beinglocated on diametrically opposite sides of the drivepin 27. The latchelement or pin 35 has an intermediate shoulder portion bearing againstthe wall of a cylindrical aperture 37 extending through the body of theeccentric. The over-all length of the latch element or pin 35 is longerthan the height of the eccentric. The latch element or pin 35 isspring-loaded by a spring 38 and is urged in a direction so that itsupper end 39 projects above the eccentric into abutting relationshipwith the underside of the drivelink end 31. The lower end 41 of thelatch element or pin 35 normally rides on the upper surface of theoutput or crank arm 1 l.

The second latch element or pin 36 also has an intermediate shoulderportion bearing against the wall of a cylindrical aperture 42 in thebody of the eccentric. This latch element or pin is spring-loaded by aspring 43 which urges the pin downwardly against the upper surface ofthe output or crank arm 11. The end 31 of the drivelink 12 has anaperture 44 which is formed by shearing and bending a section out of theplane of the link as best seen in FIG. 6. This provides an abutment edge44 against which the latch pin upper end 39 abuts on clockwise rotationof the drive mechanism. A ramp 45 leads to the abutment edge.

With the latch element or pin 35 in the relationship to the driving link12 as shown in FIGS. 1 and 6, rotation of the output or crank arm 11 ina clockwise direction results in the eccentric 28 and the link 12orbiting about the wiper motor output shaft 26, the orbital path being acircular path having a radius equal to the distance between the drivepin27 and the axis of the motor output shaft 26. This output arm radiusproduces the normal wipe pattern of the wiper blades.

Upon reverse rotation of the output or crank arm 11, the one pin 35remains in the FIG. 6 relationship to the drivelink until the other pin36 drops into a depression 47 having an abutment edge 48 and a ramp 49leading downwardly to the base of the depression, the latter beinglocated on a circle having a radius equal to the radial distance of thelatch pin 36 from the drivepin 27. When the output or crank arm 11direction is reversed, the friction between the eccentric 28 and thedrivelink 12 as well as the resistance of the pin 35 against climbingthe ramp 46 is greater than the resistance against relative movement ofthe eccentric 28 to the output arm 1 1.

As soon as the lower end 51 of the pin 36 lines up with the depression47, the spring 43 drives the pin down the ramp 49 into abutment with theedge 48 and the condition shown in FIG. 4 is reached. At the same time,the lower end 41 of the latch element or pin 35 reaches a position ofalignment with an aperture 52 in the output or crank arm 11. This occursat the start of the last half cycle of the reverse rotation of the motorshaft 26.

With the eccentric 28 locked to the outputor crank arm 11 by the latchelement 36, continued rotation of the output or crank arm 11 through thelast half cycle of the reverse rotation results in the eccentric beingmoved rotatably relative to the drivelink. The upper end 39 of the pin35 is driven downwardly under the ramp 46 on the drivelink forcing itslower end 41 into the aperture 52 so that the eccentric is locked to theoutput or crank arm 11 by both latch elements or pins 35 and 36,respectively. This occurs during the first few degrees of rotation ofthe crank arm in the last half cycle of its reverse rotation.

The end 31 of the link 12 is now rotatable relative to the eccentric 28about the cylindrical extension 29 thereon. The result is that the linkis bodily pushed away from the axis of rotation of the motor shaft 26.The axis or center of the cylindrical extension 29 in effect moves fromthe right side of the drivepin 27 axis shown in FIG. 3 to the left sideof the latter as shown in FIG. 2. Upon reaching a maximumposition ofdisplacement, the motor control circuitry is timed to stop the motorand, accordingly, the reverse rotation of the output or crank arm 11.

As seen in FIG. 5, the aperture 52 into which the lower end 41 of thelatch element or pin 35 is forced has an abutment edge 53 and a rampsurface 54 leading thereinto.

When the windshield wiper motor is started up after the wiper bladeshave been in a parked position, the first thing that happens is that thelatch element or pin 36 unlocks. That is, the lower end 51 backs awayfrom the abutment edge 48 of the depression 47. The latch pin 35,however, remains in the aperture 52 since it is blocked from moving outof the aperture by the fact that the upper end is in abutting relationto the underside of the drivelink 12. During the first half cycle of theclockwise rotation the drivelink 12 rotates around the eccentriccylindrical extension 29 until at the end of the first half cycle thelatch pin or element 35 again is in alignment with the depression 44 andthe drivelink 12. The spring 38 then becomes effective to drive the pin35 upwardly to the relationship shown in FIG. 6. The eccentric then iscompletely unlatched or unlocked from the output or crank arm 11. It isnow, however, rotatable about the drive pin 27 with the end 31 of thedrivelink and moves the latter and the wiper linkage in normal run cycleor normal wiper pattern oscillation movement.

As the eccentric 28 rotates about the drivepin 27 the latch element orpin 36 will run over the depression 47 during each revolution. It merelydrops into the recess 47 and then rides up the ramp 49 to the uppersurface of the output or crank arm 1 1 without effecting the operationof the. wiper drive mechanism. A slight clicking noise might be audibleeach time this occurs but since the wiper drive mechanism is mounted onthe engine compartment side of the fire wall of the vehicle, this noisewill not be noticeable within the passenger compartment.

It is to be understood that this invention is not limited to the exactconstruction illustrated and described above but that various changesand modifications may be made without departing from the spirit andscope of the invention as defined inthe appended claims.

We claim:

1. A windshield wiper drive mechanism having a shaf rotatable by areversible motor,

a wiper motoroutput arm on the shaft,

a drivepin fixed to the output arm,

a driving link adapted to be coupled to a wiper arm linkage,

and an eccentric interposed between the output arm and the driving link,

the eccentric being rotatable about the drivepin and the driving linkbeing rotatably coupled to the eccentric for rotation about an axisdisplaced from the axis of rotation of the eccentric about the drivepin,

the effective output arm radius in normal wipe pattern-of a wiper armbeing the distance from the shaft axis to the drivepin and in depressedpark position being this distance increased by the distance between thedrivepin and the axis of the driving link on the eccentric,

wherein the improvement comprises:

a double latch device carried by the eccentric having a pair ofspring-loaded latch elements both of which lock the output arm to theeccentric in the depressed park or maximum radius condition of theoutput arm,

the spring-loaded latch elements comprising latch pins located ondiametrically opposite sides of the drivepin,

the first one of the latch elements to unlock upon initiation of a runcycle being located on the outboard side of the drivepin relative to themotor shaft, I

the second latch element prior to initiation of the run cycle beinglocated between the drivepin and shaft,

the output arm having a ramp engageable with the first one of the latchelements upon initiation of the run cycle to drive the latter againstthe spring-loading to unlocked position,

upon initiation of the run cycle from depressed park position of thewiper arm the first one of the latch elements unlocking while the secondremains locked until the end of the first half of the run cycle isreached to restore the effective output arm radius to normal wipepattern radius,

the second latch element then unlocking the eccentric from the arm andlocking the eccentric to the drivelink,

with the eccentric locked to the drivelink relative rotation of theeccentric about the drivepin occurs and a normal wiper pattern sweep ofthe wiper arm is obtained.

2. A windshield wiper arm drive mechanism according to claim 1, inwhich:

the second latch element is spring-loaded toward the driving link and isheld in engagement with the output arm by its engagement with theunderside of the driving link until the latter is rotated to a positionin which the second latch element is aligned with an aperture in thedriving link,

the aperture having a ramp contiguous thereto effective to cam thesecond latch element out of the aperture upon reversal of the directionof rotation of the output arm.

3. A windshield wiper drive mechanism having a shaft rotatable by areversible motor,

a crank arm fixedly secured to the shaft,

a drivepin on the crank arm,

an eccentric rotatably journalled on the drivepin,

the axis of rotation of the eccentric about the drivepin being in fixed,spaced and parallel relation to the axis of the shaft,

and a driving link rotatably coupled at one end to the eccentric and atits other end to a wiper arm linkage,

wherein the improvement comprises:

a latch means including latch elements shiftable in directionsparalleling the drivepin axis to fixedly connect the eccentric to thecrank arm or to fixedly connect the eccentric to the driving linkdepending on the direction of rotation of the crank arm,

the latch elements comprising a pair of biased latch pins slidable inthe eccentric and located on diametrically opposite sides of thedrivepin about which the eccentric is rotatable,

at least one of the pins having abutting engagement with an abutment onthe crank arm in one position of the eccentric and the other havingabutting engagement with an abutment on the driving link in a secondposition of the eccentric,

and the axis of rotation of the driving link on the eccentric andtherefor the effective length of the crank arm being controlled by thelatched relationship of the eccentric to the driving link or to thecrank arm, respectively.

4. A windshield wiper drive mechanism having a shaft rotatable by areversible motor,

a crank arm fixedly secured to the shaft,

a drivepin on the crank arm,

an eccentric rotatablyjournalled on the drivepin,

the 'axis of rotation of the eccentric about the drivepin being infixed, spaced and parallel relation to the axis of the shaft, i

and a driving link rotatably coupled at one end to the eccentric and atits other end to a wiper arm linkage,

wherein the improvement comprises:

a latch means including latch elements shiftable in directionsparalleling the drivepin axis 'to fixedly connect the eccentric to thecrank arm or to fixedly connect the eccentric to the driving linkdepending on the direction of rotation of the crank arm, l the distancebetween the axis of rotation of the crank arm and the axis of rotationof the driving link on the eccentric and therefor the effective lengthof the crank arm being controlled by the latched relationship of theeccentric to the driving link or to the crank arm, respectively,

the latch elements comprising a pair of latch pins slidably journalledin the eccentric on opposite sides of the axis of rotation of the latterabout the drivepin,

a first spring means biasing one of the latch pins toward the drivelinkand a second spring means biasing the other latch pin toward the crankarms,

a first abutment on the driving link positioned to abut the one latchpin and having a ramp leading thereto,

the first abutment being effective to engage the one latch pin to lockthe eccentric to the driving link upon rotation of the crank arm innormal windshield wiper oscillation drive direction and the ramp leadingthereto being effective to cam the latch pin out of locking positionupon reverse rotation of the crank arm,

and a second abutment on the crank arm positioned to abut the otherlatch pin and having a ramp leading thereto,

the second abutment being effective toengage the other latch pin to lockthe eccentric to the crank arm upon reverse rotation of the latter whichlocking action occurs at a position of the wiper arm corresponding tothe start of a wipe cycle,

further rotation in reverse direction causing the eccentric to bodilyshift the driving link away from the crank arm axis of rotation to drivethe wiper arm below its normal wipe cycle start position into adepressed park position.

1. A windshield wiper drive mechanism having a shaft rotatable by areversible motor, a wiper motor output arm on the shaft, a drivepinfixed to the output arm, a driving link adapted to be coupled to a wiperarm linkage, and an eccentric interposed between the output arm and thedriving link, the eccentric being rotatable about the drivepin and thedriving link being rotatably coupled to the eccentric for rotation aboutan axis displaced from the axis of rotation of the eccentric about thedrivepin, the effective output arm radius in normal wipe pattern of awiper arm being the distance from the shaft axis to the drivepin and indepressed park position being this distance increased by the distancebetween the drivepin and the axis of the driving link on the eccentric,wherein the improvement comprises: a double latch device carried by theeccentric having a pair of spring-loaded latch elements both of whichlock the output arm to the eccentric in the depressed park or maximumradius condition of the output arm, the spring-loaded latch elementscomprising latch pins located on diametrically opposite sides of thedrivepin, the first one of the latch elements to unlock upon initiationof a run cycle being located on the outboard side of the drivepinrelative to the motor shaft, the second latch element prior toinitiation of the run cycle being located between the drivepin andshaft, the output arm having a ramp engageable with the first one of thelatch elements upon initiation of the run cycle to drive the latteragainst the spring-loading to unlocked position, upon initiation of therun cycle from depressed park position of the wiper arm the first one ofthe latch elements unlocking while the second remains locked until theend of the first half of the run cycle is reached to restore theeffective output arm radius to normal wipe pattern radius, the secondlatch element then unlocking the eccentric from the arm and locking theeccentric to the drivelink, with the eccentric locked to the drivelinkrelative rotation of the eccentric about the drivepin occurs and anormal wiper pattern sweep of the wiper arm is obtained.
 2. A windshieldwiper arm drive mechanism according to claim 1, in which: the secondlatch element is spring-loaded toward the driving link and is held inengagement with the output arm by its engagement with the underside ofthe driving link until the latter is rotated to a position in which thesecond latch element is aligned with an aperture in the driving link,the aperture having a ramp contiguous thereto effective to cam thesecond latch element out of the aperture upon reversal of the directionof rotation of the output arm.
 3. A windshield wiper drive mechanismhaving a shaft rotatable by a reversible motor, a crank arm fixedlysecured to the shaft, a drivepin on the crank arm, an eccentricrotatably journalled on the drivepin, the axis of rotation of theeccentric about the drivepin being in fixed, spaced and parallelrelation to the axis of the shaft, and a driving link rotatably coupledat one end to the eccentric and at its other end to a wiper arm linkage,wherein the improvement comprises: a latch means including latchelements shiftable in directions paralleling the drivepin axis tofixedly connect the eccentric to the crank arm or to fixedly connect theeccentric to the driving link depending on the direction of rotation ofthe crank arm, the latch elements comprising a pair of biased latch pinsslidable in the eccentric and located on diametrically opposite sides ofthe drivepin about which the eccentric is rotatable, at least one of thepins having abutting engAgement with an abutment on the crank arm in oneposition of the eccentric and the other having abutting engagement withan abutment on the driving link in a second position of the eccentric,the distance between the axis of rotation of the crank arm and the axisof rotation of the driving link on the eccentric and therefor theeffective length of the crank arm being controlled by the latchedrelationship of the eccentric to the driving link or to the crank arm,respectively.
 4. A windshield wiper drive mechanism having a shaftrotatable by a reversible motor, a crank arm fixedly secured to theshaft, a drivepin on the crank arm, an eccentric rotatably journalled onthe drivepin, the axis of rotation of the eccentric about the drivepinbeing in fixed, spaced and parallel relation to the axis of the shaft,and a driving link rotatably coupled at one end to the eccentric and atits other end to a wiper arm linkage, wherein the improvement comprises:a latch means including latch elements shiftable in directionsparalleling the drivepin axis to fixedly connect the eccentric to thecrank arm or to fixedly connect the eccentric to the driving linkdepending on the direction of rotation of the crank arm, the distancebetween the axis of rotation of the crank arm and the axis of rotationof the driving link on the eccentric and therefor the effective lengthof the crank arm being controlled by the latched relationship of theeccentric to the driving link or to the crank arm, respectively, thelatch elements comprising a pair of latch pins slidably journalled inthe eccentric on opposite sides of the axis of rotation of the latterabout the drivepin, a first spring means biasing one of the latch pinstoward the drivelink and a second spring means biasing the other latchpin toward the crank arms, a first abutment on the driving linkpositioned to abut the one latch pin and having a ramp leading thereto,the first abutment being effective to engage the one latch pin to lockthe eccentric to the driving link upon rotation of the crank arm innormal windshield wiper oscillation drive direction and the ramp leadingthereto being effective to cam the latch pin out of locking positionupon reverse rotation of the crank arm, and a second abutment on thecrank arm positioned to abut the other latch pin and having a rampleading thereto, the second abutment being effective to engage the otherlatch pin to lock the eccentric to the crank arm upon reverse rotationof the latter which locking action occurs at a position of the wiper armcorresponding to the start of a wipe cycle, further rotation in reversedirection causing the eccentric to bodily shift the driving link awayfrom the crank arm axis of rotation to drive the wiper arm below itsnormal wipe cycle start position into a depressed park position.